A sawing system for singulating or dicing electronic components, such as semiconductor substrates or packaged semiconductor devices on substrates, comprises at least a spindle system including a sawing blade and a carrier support such as a chuck table. The motion axis of the spindle system is orthogonal to the motion axis of the chuck table and a theta axis table is located on top of the chuck table. The spindle system typically includes either one or two high-speed rotating shafts with a sawing blade each. In a dual spindle system, two parallel spindles are arranged either facing each other or next to each other facing the same direction.
Dicing may be performed on the semiconductor substrate in one direction by moving the chuck table under a spindle axis while the sawing blade is cutting the semiconductor substrate on a carrier, such as a saw jig, on the theta axis table of the chuck table. The spindle axis may index line by line to cut along all the cutting lines required in one direction. Next, the theta table on the chuck table rotates 90 degrees about the theta axis to perform dicing in a direction orthogonal to the first direction. Accordingly, the semiconductor substrate is singulated into rectangular units.
FIGS. 1 to 3 are plan views of samples of semiconductor substrates which need to be diced along cutting lines. FIG. 1 illustrates a leadframe with two types of alignment marks 101, 103 along its cutting lines. In another leadframe as shown in FIG. 2, alignment marks are located about the cutting lines. The cutting lines are virtual cut lines 105, 107 along the length and width of the leadframe. As there is a predetermined dimensional relationship with the virtual cutting lines, the cutting lines can be determined after recognizing the corresponding alignment marks. FIG. 3 shows a map of virtual cutting lines on a wafer which are denoted as cutting lines 109, 111.
For more accurate dicing, a pattern recognition (PR) camera is mounted on the spindle axis to recognize the alignment marks such as those shown in FIGS. 1 to 3 on the semiconductor substrate before dicing. In this way, accurate dicing can be achieved by determining an alignment of the substrate and adjusting its offset in the X-Y-θ axes prior to dicing. There is however a drawback in using a PR camera mounted on the spindle axis in that the working sequence from substrate loading, PR alignment, dicing to unloading has to be sequential. This prolongs the cycle time for dicing a substrate.
One way to reduce the cycle time is to have a separate vision station for PR alignment. The separate station is located either at one end of a sawing zone or in between the sawing zone and a loading/unloading zone. A disadvantage of this approach is that the water for cooling the sawing blades and for washing away the debris from dicing the second substrate may contaminate the first substrate as it passes through the sawing zone. Another disadvantage is that an additional motion axis is required for the separate vision station. This means increased costs and space required for incorporating an additional chuck table and the related mechanisms to move the chuck table along that axis. Furthermore, cycle time is increased as each semiconductor substrate has to move some distance from the substrate loading/unloading station to the vision alignment zone for alignment before dicing. One prior art which uses the sawing system described above is US Patent Publication No. 2002/0184982 entitled “Bidirectional Singulation Saw and Method”.
Another prior art example of a sawing system is disclosed in U.S. Pat. No. 6,826,986 entitled “Bi-directional Singulation System and Method” which has a separate vision system for PR alignment. Unlike the aforesaid sawing system, the vision alignment zone of the sawing system is located between the sawing zone and the loading/unloading zone. Thus, the substrates do not have to pass through the sawing zone for vision alignment at the vision alignment zone. In this way, the substrates are not contaminated by water and debris in the sawing zone. This system also has the disadvantages of having an additional motion axis for moving the work chucks to the separate vision alignment zone and that the semiconductor substrates are still required to move some distance from the substrate loading/unloading station to the vision alignment zone for positioning before dicing.
FIG. 4 is a plan view of an exemplary singulation system 10 in the prior art which does not require an additional motion axis for moving a chuck table to a separate vision alignment zone. The singulation system 10 comprises two cameras. Each camera is mounted and carried on a spindle axis next to a cutting blade. A substrate 12 which is to be singulated is placed onto a rotary chuck table 14 positioned below a first spindle 16 and a second spindle 18. The substrate 12 moves in a Y-axis below and across the X-axes of the first and second spindles 16, 18. A first alignment vision camera 20 and a second alignment vision camera 22 are mounted respectively on the first and second spindles 16, 18. The first alignment vision camera 20 and the second alignment vision camera 22 have first and second viewfinders 24, 26 respectively for capturing images of the substrate 12. The cameras can be adjusted along the X-axes of the first and second spindles 16, 18 for locating the alignment markings on the substrate 12. The chuck table 14 is rotatable to position the substrate 12 in another orientation for indexing the substrate 12 along the Y-axis for viewing by the cameras.
FIGS. 5A to 5D are plan views of a leadframe 28 showing a conventional method for pattern recognition (PR) alignment of the leadframe 28 on the chuck table 14 by “stop and grab” means using the singulation system 10 of FIG. 4. The leadframe 28 is positioned in a first or width orientation as shown in FIG. 5A. The first and second cameras 20, 22 move to positions in the X-direction along the first and second spindles such that their field of views (FOVs) may locate a first pair of alignment marks at the top two corners of the leadframe 28, and then “grab” or capture the images of the marks. In FIG. 5B, the chuck table 14 moves in the Y-direction and transports the leadframe 28 to a position where the first and second cameras 20, 22 may locate in their FOVs a second pair of alignment marks which are at the bottom corners of the leadframe 28 before capturing the images of the marks.
FIG. 5C shows the leadframe 28 in a second or length orientation after it has been rotated 90° by the chuck table 14. The PR alignment process may be repeated as in FIG. 5A for the top pair of alignment marks along the length of the leadframe 28. Next, the chuck table 14 moves in the Y-direction and transports the leadframe 28 to another position, as shown in FIG. 5D, so that the bottom pair of alignment marks fall within the FOVs of the cameras which locate the alignment marks accordingly as in FIG. 5B. Once sufficient information has been collected of the corner alignment marks, the positions and orientations of the cutting lines on the leadframe 28 can be estimated and stored for the cutting operation.
FIG. 6 illustrate plan views of a wafer 28′ which show the conventional “stop and grab” means according to FIGS. 5A to 5D to perform PR alignment on a wafer 28′ using the singulation system 10 of FIG. 4. As this method of PR alignment again involves stopping the chuck table before capturing the images, cycle time is comparatively long. Therefore, it would be desirable to shorten the cycle time of the singulation process.